The invention relates to a brake system for motor vehicles using an actuation unit which can be actuated by an actuation pedal, the actuation unit consisting of a pneumatic brake booster and a master brake cylinder, to which the wheel brakes are connected, where the control valve of the brake booster can be controlled independently of the driver's will by means of a solenoid, by means of whose armature one of the sealing seats of the control valve can be actuated, with a brake pressure controller, which is supplied with a control difference from a desired brake pressure and an actual brake pressure and from whose output variable, corresponding to a desired armature travel, a signal is subtracted, which corresponds to the actual armature travel, and where the second control difference thus generated is applied to a positioning controller which influences the position of the control valve, where the output variable of the positioning controller corresponds to the electrical current which is to be applied to the solenoid.
Such a brake system is known from International Patent Application WO 95/03196. The mentioned document contains, however, no concrete indications how the brake system described therein could be used for a deceleration control, proportional to the force of actuation.
In German Patent DE 33 25 854 C2 a brake controller for the control of a vehicle brake system has been disclosed, which works in cooperation with a brake booster which can be controlled independently of the driver's will, preferably electrically. The mentioned electrical control occurs by means of a control valve, located outside of the brake booster, which influences a pneumatic difference pressure which can be applied to the amplifier housing and which receives control signals of a data processing installation which processes, as input variables, signals of two sensor setups. The first sensor setup consists of a velocity sensor, whose signals are differentiated to determine vehicle decelerations. The second sensor setup consists of a force sensor, which is used for the determination of the actuation force applied at an actuation pedal. The second sensor setup can be replaced, as selected, by a third sensor setup, which determines the initial force of the brake booster, which is proportional to the hydraulic pressure or brake pressure which is generated in a master brake cylinder which is connected after the brake booster. The data processing installation contains statistical parameter lines, from which the desired values of the deceleration are determined.
In the already known controller, a drawback results from the errors in the control which occur during rapid operation by the driver, as a result of the use of the statistical characteristic lines, and which do not correspond to the natural desired behavior of the brakes.
Therefore, the problem of the present invention is to propose measures which make it possible, in the generic brake system, to obtain a problem-free post-control as well as a more slow, and a more rapid, actuation process. In addition, the desired vehicle deceleration should be reached rapidly, independently of influences which lead to a decrease in the deceleration, such as, for example, additional loading of the vehicle, trailer operation, fading/frictional losses or slope drag force in the case of downward trips.